Escape	Description
\\	backslash
\a	alert (BEL)
\b	backspace
\c	suppress trailing newline
\f	form feed
\n	new line
\r	carriage return
\t	horizontal tab
\v	vertical tab

Form	Description
${var}	Substitue the value of var.
${var:-word}	If var is null or unset, word is substituted for var. The value of var does not change.
${var:=word}	If var is null or unset, var is set to the value of word.
${var:?message}	If var is null or unset, message is printed to standard error. This checks that variables are set correctly.
${var:+word}	If var is set, word is substituted for var. The value of var does not change.

#!/bin/sh

a=10
echo -e "Value of a is $a \n"

						

Value of a is 10

						

Value of a is 10\n

						
Syntax:

`command`

						
Example:

#!/bin/sh

DATE=`date`
echo "Date is $DATE"

USERS=`who | wc -l`
echo "Logged in user are $USERS"

UP=`date ; uptime`
echo "Uptime is $UP"

						

Date is Thu Jul  2 03:59:57 MST 2009
Logged in user are 1
Uptime is Thu Jul  2 03:59:57 MST 2009
03:59:57 up 20 days, 14:03,  1 user,  load avg: 0.13, 0.07, 0.15

						
Example:

#!/bin/sh

echo ${var:-"Variable is not set"}
echo "1 - Value of var is ${var}"

echo ${var:="Variable is not set"}
echo "2 - Value of var is ${var}"

unset var
echo ${var:+"This is default value"}
echo "3 - Value of var is $var"

var="Prefix"
echo ${var:+"This is default value"}
echo "4 - Value of var is $var"

echo ${var:?"Print this message"}
echo "5 - Value of var is ${var}"

						

Variable is not set
1 - Value of var is
Variable is not set
2 - Value of var is Variable is not set

3 - Value of var is
This is default value
4 - Value of var is Prefix
Prefix
5 - Value of var is Prefix